Abstract

With a closely related pairing a certain part of the genes passes into a homozygous state and is phenotypically displayed. In the descendants of heterozygous carriers of unwanted mutations, the disguised action of dominant alleles disappears, which is the cause of the preservation and spread of harmful recessive alleles in the population. When inbreeding, the formation of homozygous individuals is possible, which will detect the effect of unwanted chromosomal damage in them.

The purpose of the research is to evaluate the karyotype variability of the first-born cows of Ukrainian Red-and-White diary breed of different levels of kinship. The object of research was the breeding stock of Ukrainian Red-and-White diary breed, which is breeding in the state enterprise "DG" Khrystynivske" of the Institute of Animal Breeding and Genetics named after M.V.Zubets NAAS. On the basis of the analysis of materials of zootechnical records from computer information management system dairy cattle "Intesel Orsek" selected cows with different degrees of kinship.

The cytogenetic analysis was performed in the Department of Genetics and Biotechnology of the Institute of Animal Breeding and Genetics named after M.V.Zubets of NAAS with the use of special techniques and related equipment. For the preparation of chromosomes, the culture of leukocytes of peripheral blood of animals was used. Short-term culture was prepared using Moorhead et al.

As a result of studies of the karyotype variability of cows of Ukrainian Red-and-White diary breed of different levels of affinity, no gross constitutional anomalies of the chromosomal set were revealed in any cow. The genomic type anomalies (aneuploidy and polyploidy) and structural aberrations of chromosomes (fragments, ruptures, association of chromosomes) have been identified. The average level of aberrant cells was highest in near-related animals, which is significantly higher than those observed in outbreed cows by 6.0%, with a distant and moderate degree of inbreeding – by 6.4 and 6.7 at P < 0.999 in all cases. The frequency of aneuploidy cells in closely related primates exceeds this rate in outbred animals with an unreliable difference. The same insignificant difference in the level of aneuploid cells is also found between the outbred and inbred individuals from the moderate and remote degree of affinity. The proportion of polyploid cells in all tested cows does not exceed one percent, which is the norm for bovine cattle. The difference between groups of outbred and inbred animals is unreliable. The frequency of cells with chromosomal rupture ranges from 2.31% in cows with distant cows to 5.50% in animals with close inbreeding, on average, and the difference between these indices (3.19%) is statistically significant (P < 0.999), as well as The difference between the outbreed and the animals with moderate inbreeding (P < 0.95).

In order to assess the reproductive ability of cows of different degrees of affinity, three groups have been formed taking into account functional disorders of the reproductive system: Group I – animals with the presence of stillbirths and spontaneous miscarriages; II group – cows with a service period after the first lactation for at least 150 days; Group III – cows that have the service period after the first lactation 51–90 days (a conditional control group). Of the 103 studied cytogenetic indices in cows of different degrees of affinity, 24 cows (23.3% of the investigated livestock) were caught in a group of animals with impaired reproductive ability (Group I) The largest share in this group was cows obtained as a result of remote inbreeding (11.6%). In the group of cows with a service period of more than 150 days the most were outbreds (16.5%). In the third group (with the service period at cows 50-90 days), the most outbreed cows and animals obtained as a result of remote inbreeding were found. Their shares were the same and amounted to 8.7% each. Thus, the dependence of the condition of the reproductive system of cows on their affinity is not established.

The incidence of cells with genomic disorders and structural aberrations of cows with disturbed reproductive ability, irrespective of the degree of their inbreeding, is 4.2–3.5% higher (P < 0.999) than in cows with normal reproductive function.

Outbred and inbred cows have been ranked according to genetic risk levels: low genetic risk (RBD), average genetic risk (SRHR) and high genetic risk (RBD) (Fig. 3). Indicators of the frequency of genomic and chromosomal mutations of the karyotype express the level of general resistance and the potential for the implementation of vital functions of the animal organism. An analysis of the genetic structure of the population according to the level of genetic risk has shown that in the group of low genetic risk, the largest share is cows without abnormalities in the reproductive system. The cytogenetic study of cows allows not only to evaluate the saturation of undesirable aberrations of the chromosomes of this herd of Ukrainian red-billed milk breed, but also allows us to use the results obtained to predict at an early age the reproductive capacity of cows.